It is known that propeller-type propulsion systems, for example turboprops with a single propeller or prop fans with contra-rotating propellers, display better energy efficiency than turbine engines.
However, most of existing aircraft are propelled by turbine engines which are therefore, on the one hand, greedy for fuel and, on the other hand, sources of environmental pollution through what they emit into the atmosphere.
Hence, as far as saving energy and reducing environmental pollution are concerned, it would be more advantageous for aircraft to be equipped with propeller-type propulsion systems rather than turbine engines.
However, in operation, propeller-type propulsion systems are even more noisy than turbine engines, which means that the advantage in terms of energy saving and reduction in environmental pollution from their emissions which are enjoyed when turbine engines are replaced by propeller-type propulsion systems, would be accompanied by the disadvantage of an increase in noise pollution. The noise pollution thus reached would be unacceptable and, in any event, difficult to reconcile with the legislation currently in force.
Furthermore, aircraft comprising:                at least one turbine engine mounted at the rear of the aircraft, on the back thereof; and        a cell, the rear part of which comprises a horizontal empennage and two vertical empennages positioned one at each end of said horizontal empennage, said rear part forming a barrier to the noise generated downwards by said turbine engine,are already known, for example from GB-1 397 068.        
Of course, in a layout such as this, the axis of said turbine engine is parallel to the longitudinal axis of the aircraft which means that the noise generated by said engine and which, as is known, is emitted toward the front and toward the rear of this engine, spreads toward the front and toward the rear of said aircraft, only some of this noise being screened in the downwards direction by said screening surface of the rear part of the cell, provided that said horizontal empennage is positioned to the rear of the outlet of the nacelle of said turbine engine. The overall efficiency of the screen formed by the rear part of the cell is therefore not optimized.